An electric vehicle having left and right electric motors for driving left and right drive wheels, left and right brakes for individually regulating the speeds of the left and right drive wheels, and a control part for controlling the speeds of the left and right electric motors is proposed for example in JP-A-2002-142306.
Generally, the speeds of the electric motors are directly controlled on the basis of an accelerator angle. However, in the case of the electric motors disclosed in JP-A-2002-142306, for example in controlling the left electric motor, control is carried out whereby when a left brake angle is large a left motor control value is lowered, and when a right brake angle is large the left motor control value is lowered further to take into account this right brake angle. And similar control is carried out for the right electric motor. Thus, the waste of rotating the electric motors at high speeds while braking is applied is avoided.
Also, normally, the vehicle sometimes sways due to the speeds of the left and right electric motors becoming unbalanced during operation. However, in the case of the electric motors in JP-A-2002-142306, because not only the left brake angle but also the right brake angle is taken into account with respect to the left electric motor, there ceases to be this concern, and irrespective of the state of the traveling surface speed regulation is easy and the vehicle has a smooth traveling characteristic.
Next, the action of a brake lever disclosed in JP-A-2002-142306 will be explained, on the basis of FIG. 10A and FIG. 10B.
Left and right brake levers 100L, 100R are control levers with which it is possible to switch continuously from brake percentage zero % (no braking) to brake percentage 100% (full braking). The position of the left brake lever 100L is monitored with a brake potentiometer 102L. The position of the right brake lever 100R is monitored with a brake potentiometer 102R.
FIG. 10B is a graph showing the relationship between the positions of the left and right brake levers 100L, 100R and the output voltages of the left and right brake potentiometers 102L, 102R. When a brake percentage is zero %, the output voltage of the respective brake potentiometer 102L, 102R is zero V. When a brake percentage is 100%, the output voltage of the respective brake potentiometer 102L, 102R is 5V.
The brake potentiometers 102L, 102R are analog sensors, and have the merit that they can continuously obtain output voltages corresponding to the positions of the brake levers 100L, 100R easily.
However, because they are analog sensors, there is unavoidable dispersion among sensors, and zero point adjustment must be carried out for each individual sensor, and the time and cost entailed in this adjustment mount up. Also, analog sensors are generally somewhat expensive, and this has been a cause of increased cost of the electric vehicle, so that technology for making the detection of the brake angles cheaper has been awaited.